<Basically this dude aggressively pursued her even though she already had/has a girlfriend> Some people can't take no for an answer. They think they can wear you down until you change your mind and don't see that behavior as abnormal. But that's only part of the problem, this is the rest:

<Do they get off on shaming, guilt-tripping, and forcing > While some probably do, the rest know they can get away with doing that and have no problem using those tools. And they have help from LGB and straight people who drank the gender kool-aid. Your coworker exposed herself as not being a member of the queer theory cult, I.E. sexuality = gender/identity attraction, and that monogamy is bad because "heteronomativity"

please let her know we are here, there's plenty to read even if we are a small group.

As a side note: <what is it with poly being pushed so hard too?> That's the Q influence, monogamy needs to be deconstructed because of heteronormativity and other "queer" relationships need to be celebrated, like poly.